Invoice files: PDF, XML and the e-invoice

Everyone who can read the client's invoices sees and downloads the files; only owners and admins see Try again. The first time someone who may edit invoices (owner, admin, accountant, bookkeeper) opens or downloads the PDF or XML, the invoice counts as handed out: from then on Void is refused (§ 14c UStG) and only a cancellation or corrective invoice remains.
After Assign number and lock the files are made in the background. While you read "The PDF is being created and archived unalterably." do nothing: the page asks again by itself and switches over. Then it reads "PDF archived unalterably, SHA-256 ..." with Open invoice PDF and two download buttons, Download PDF and Download XML.
If it reads "The PDF could not be created. Sending stays blocked until it is archived.", the invoice itself is fine (number and booking exist) but cannot be sent yet. An owner or admin chooses Try again. If "The new attempt could not be started." appears, try again a little later.
An XML (the e-invoice) is made for invoices only, not for quotations, order confirmations or delivery notes. A customer with a Leitweg-ID gets an XRechnung 3.0. A business customer in Germany gets the client's default: ZUGFeRD (EN 16931, the XML sits inside the PDF and is also offered as a file) or XRechnung. A private person gets a PDF only. A business customer abroad gets a PDF only, unless the switch below is on (then ZUGFeRD).
The line above the files says which format was made and who checked it: "checked by the KoSIT validator before numbering", or in red "checked by the EN 16931 core rules before numbering (the KoSIT validator was unreachable)". Then E-invoice valid or E-invoice invalid, and a count of warnings with their rule codes. Warnings do not stop anything. An invalid e-invoice is never issued: finalize is refused and no number is used (see the page on invoices that will not finalize).
Set it up in Settings, Company profile tab: Default e-invoice format (ZUGFeRD or XRechnung), the switch E-invoice (ZUGFeRD EN 16931) for business customers abroad too, and the Invoice contact (contact person, phone, e-mail) that the e-invoice needs. On the customer under Contacts: Business customer (B2B) and Leitweg-ID (public sector). In the invoice editor Customer type Company or Private person must be chosen.
File names are the invoice number plus .pdf or .xml; in the invoice mail a slash in the number becomes a hyphen, and both stored files are attached. Preview (PDF) on a draft is only a watermarked sketch and is never stored.